The invention relates in general to the field of pressure measurement and in particular to a pressure indicator for use in a fluid-filled vibration isolator.
It is very important in many fluid-based devices that the fluid volume and fluid pressure be maintained within the device. If a sufficient volume of fluid is lost from the device, or the device is for some other reason not sufficiently full, the operation of the device may be seriously impaired. Similarly, if sufficient pressure is not maintained within the device, certain devices may experience cavitation within the fluid, thereby impairing performance. It is, of course, intuitive that loss of fluid volume and loss of fluid pressure will often occur together. Accordingly, it is often advantageous to incorporate a pressure gauge into the design of such devices in order to monitor the condition of the device.
Significant effort has been directed, therefore, toward the design of effective devices for measuring the pressure in such fluid-based systems. These devices can also be used to determine whether the pressure within a vessel or fluid path is sufficient for proper operation of a mechanical device or system. Such pressure-measurement devices are also useful for determining whether the pressure in a vessel is within the acceptable mechanical limits of the vessel.
One known design for measuring pressure in a vessel is built around a sealed elastomeric diaphragm. The diaphragm is exposed to the fluid pressure on one side, and a reference pressure on the opposite side. With this device, the pressure in the vessel can be determined from the displacement of the diaphragm. In the most common design of this type, the reference pressure employed is atmospheric air pressure. In designs intended for measurement of higher pressures, the force of the pressure on the diaphragm is opposed by a spring.
A second known design uses a piston and cylinder apparatus in place of the diaphragm described above. In this design, the outside edge of the piston is sealed with an o-ring. As with the above-described design, the force of the fluid pressure may be opposed by a spring acting on the piston.
Pressure gauges and transducers traditionally employed for pressure measurement incorporate several limitations that make them poorly suited for use with certain devices. First, traditional commercially available pressure transducers incorporate organic membranes to contain the fluid against pressure. Although these types of membranes are suitable for containing certain types of fluids, certain other types of fluids, particularly fluorocarbon based fluids, can diffuse through these membranes at an unacceptable rate. Second, for the same reason that organic membranes are problematic, traditional methods of sealing pressure lines, such as organic O-rings and gaskets, may be unacceptable options. Third, even without respect to diffusion concerns, it is known that every pressure seal added to a design is an additional failure mode for the device, reducing the reliability of the device as a whole.
The present invention disclosed herein comprises an improved pressure indicator designed to overcome many of the shortcomings inherent in prior designs. First, the design makes use of a metal diaphragm in place of the organic diaphragm found in traditional designs. Second, in at least one embodiment the case of the pressure indicator of the present invention is hermetically sealed, thereby eliminating any concern regarding diffusion through or leakage around o-rings or gaskets. Third, certain embodiments of the pressure device of the present invention are contained completely within the body of the pressure vessel, so that there are no additional pressure connections to increase the potential for failure of the device.
A pressure indicator according to the present invention is designed to be used to monitor the pressure of the fluid in a vessel. One embodiment of the present invention comprises a sealed housing having at least one flexible surface and a spring disposed to act against the flexible surface and having a spring rate such that the flexible surface will be deflected in a convex manner whenever the pressure external to the indicator falls below a selected level. A second embodiment comprises a sealed bellows having at least one closed end and a spring disposed to act against the closed end of the bellows such that the length of the bellows will increase as the pressure external to the indicator decreases.
One embodiment of the present invention comprises a closed pressurized gas volume behind a dimpled metal diaphragm. In normal operation, the force of the fluid pressure acting on the external surface of the diaphragm overcomes the force of the gas pressure acting on the internal surface of the diaphragm to hold the diaphragm in a concave geometry. In the event of a sufficient loss of fluid pressure, the force of the gas pressure acting on the internal surface of the diaphragm will overcome the force of the fluid pressure acting on the external surface of the diaphragm, thereby moving the diaphragm into a convex geometry. In certain embodiments, a viewing window disposed in the side of the vessel can be used to view the pressure indicator and determine whether the indicator diaphragm is disposed in a concave or convex shape.
In certain embodiments of the present invention, a pressure indicator as disclosed herein is incorporated into the design of a liquid inertia vibration isolator in order to indicate pressure changes within the isolator. A pressure indicator of the present invention is particularly useful in this context as fluids commonly used in such vibration isolators are known to permeate through elastomers and polymers traditionally used in pressure indicating devices.
The present invention overcomes many limitations present in prior devices. The metal diaphragm used in place of the organic diaphragm found in traditional designs overcomes any concern for diffusion through the diaphragm. Hermetically sealed embodiments of the present invention eliminate any concern regarding diffusion through or leakage around o-rings or gaskets. Finally, those embodiments contained completely within the body of the pressure vessel eliminate any possibility of fluid loss from the device through the pressure indicator.